1. Field of the Invention
This invention relates to a vibration isolation mount for a hand-held, motor-driven power tool. In particular, it relates to a vibration isolation mount for a chain saw.
2. Description of the Prior Art
Hand-held, motor-driven power tools, particularly chain saws driven by an internal combustion engine, are subject to vibration caused by the non-uniformity of the drive and mass forces acting on the unit. These vibrations of the unit are transmitted to the hands and body of the operator and may cause early fatigue of the operator, numbness in the arms of the operator, and, over a long term of use, may injure the health of the operator. Many attempts to overcome this problem are disclosed in the prior art.
Rauh, U.S. Pat. No. 3,409,056, discloses a portable chain saw having a drive engine and a support handle unit having a transverse and a longitudinal handle rigidly interconnected with vibration damping bushings at the ends of the transverse handle and the rear end of the longitudinal handle which connect the handle to the saw unit and eliminate vibration. The vibration damping bushings are rubber-like resilient mountings, the axes of which are parallel to the axis of rotation of the engine crankshaft so as to insure a strong damping action and cause the mountings to be stressed mainly in shear and less in compression or tension.
Frederickson et al, U.S. Pat. No. 3,542,095, discloses a chain saw comprising a first assembly including an engine, a guide bar and a drive system and a second assembly including a fuel tank and carburetor. Vibration isolating means are interposed between the two assemblies. A handle network defines a cage-like structure, within which the first assembly is resiliently supported by vibration isolating units. The vibration isolating units define a generally triangular shock absorbing network more or less aligned with a principal vibration plane and disposed about the center of mass of the vibration generating assembly (the center of mass being more or less adjacent to the axis of rotation of the engine crankshaft in many commercial chain saws).
Lange, U.S. Pat. No. 3,620,269, discloses a chain saw wherein vibrations from the engine to the handle are absorbed by forming the handle with a core which is rigidly attached to the chain saw body and a sheath which surrounds the handle in spaced apart relation and is held relative to the core by a spacer of yieldable material. This spacer can take the form of a plurality of spaced rings of rubber or synthetic material having elastic properties. The damping action of the spacer can be varied to a desired degree by a choice of the resiliency of the elastic material, the radial distance between the core and the sheath, the length of the rings and the length of the intervals between the rings.
Sherwood, Jr. et al, U.S. Pat. No. 3,637,029, discloses a hand-held power tool comprising an internal combustion engine on which a power tool is mounted and by which it is driven. The engine is mounted by vibration isolators on an essentially rigid supporting structure comprising a base portion, a front handle and a rear handle. Four vibration isolators are so arranged as to isolate the supporting structure from vibration of the engine while providing effective control of the tool by an operator for holding the supporting structure by the front and rear handles. The vibration isolators are in the form of hollow barrel-shaped bodies of elastomeric material. The four vibration isolators supporting the engine are located at the apices of a tetrahedron. Three of the isolators are located at the front of the engine with two of them below the engine and on opposite sides while the third is located above the engine and at one side. The fourth vibration isolator is located at the rear of the engine. Two of the isolators are positioned with their axes approximately horizontal and parallel with the engine crankshaft while the other isolators are positioned with their axes vertical. In all instances, the axes of the isolators are perpendicular to a fore-and-aft direction (the axis of the engine cylinder). By reason of the isolators having a higher spring constant in a direction axially of the isolator and a lower spring constant in a direction perpendicular to the axis, the transmission of engine vibration to the supporting structure is effectively attenuated.
Frederickson et al, U.S. Pat. No. 3,698,455, discloses a vibration isolation and bumper system for a chain saw. In particular, a first assemblly generates mechanical vibrations and includes an internal combustion engine, a cutting chain with a guide bar and a drive system. A second assembly comprises an inertia mass and may include a fuel tank and a carburetor. Vibration isolation means connect the two assemblies and the second assembly may include a handle network provided to define a cage-like structure. The first assembly is resiliently supported within the cage-like structure by the vibration isolation means and bumper devices. The axis of rotation of the crankshaft within the engine and the cutting plane of the overall saw are arranged to direct a substantial portion of the total vibrational energy along a primary plane of vibration. The vibration isolation means and bumper devices are aligned with and cooperate to absorb shock energy directed along this primary plane.
Makinson et al, U.S. Pat. No. 3,728,793, discloses a chain saw having means for damping or reducing shocks and vibrations transmitted between the chain saw body and the operator. The chain saw has two separate handles, one near the front and one near the rear. Each of the handles has shock-absorbing or damping means at the end portion thereof connected to the engine. For the front handle, the upper shock-absorbing means for the upper end of the handle is postioned at an angle to the vertical and, preferrably, generally perpendicular to the general direction in which the operator's arm extends back and away from the handle. This places the shock-absorbing or damping element in shear. The lower shock-absorbing means for the lower end portion of the front handle allows limited pivotal movement of the front handle relative to the chain saw body, with the shock-absorbing or damping element placed in torsion. For the back handle, both upper and lower shock-absorbing means connecting the handle to the chain saw extend generally perpendicular to the longitudinal extent of the chain saw and to the operator's arm, with the shock-absorbing or damping element placed in shear.
Notaras et al, U.S. Pat. No. 3,733,700, discloses a dual grip handle for power tools, the grip comprising a first handle member flexibly connected to the power unit, a second handle member flexibly connected to the power unit, and a means for flexibly interconnecting the first and second handle members.
Bailey, U.S. Pat. No. 3,845,557, discloses a chain saw anti-vibration system wherein a vibration generating assembly is connected to a support assembly by a plurality of vibration isolation assemblies. Each vibration isolation assembly includes a first cup mounted upon one of the vibration generating assembly or the support assembly and a post mounted upon the other of the vibration generating assembly or the support assembly. The post is dimensioned to be coaxially received within the interior of the first cup. Each of the vibration isolation assemblies includes a second cup of an elastomeric material dimensioned to contiguously fit within the interior of the first cup. The second cup is provided with at least one elastomeric circumferentially inwardly projecting ring dimensioned to engage under hoop tension at least a portion of the exterior surface of the post whereby relative vibrations between the post and the first cup will be attenuated by the elastomeric second cup. Moreover, two annular rings formed on the exterior of the second cup serve to contact the interior surface of the first cup. By this design, the vibration mounts initially resist vibrational forces by elastomeric bending (shearing) of the second cup, which with increasing magnitude of the vibrational force makes a transition to solid compression of the second cup. Additionally, the mounts are oriented to have their axes lie in the primary plane of vibration, which is substantially perpendicular to the crankshaft axis.
Schulin, U.S. Pat. No. 3,845,827, discloses a portable tool, especially a chain saw, having a handle connected to the tool through a spring elastic connector. A compensator mass is connected to the handle through another spring elastic connector and the compensator mass is free to oscillate relative to the handle. The oscillation of the compensator mass is in counter phase to that of the tool. The handle is elasticly coupled to both tool and compensator mass and located at approximately the vibration node or nodal point. The handle is therefor subject to small amplitudes of movement.
Nagashima, et al, U.S. Pat. No. 3,945,119, discloses a chain saw comprising an engine unit including an engine, a fuel tank, an oil tank and a chain driving system which is mounted on a handle assembly consisting of a front handle, a rear handle, and a handle connecting member interconnecting the front and rear handles and supporting the bottom of the engine unit through three vibration isolators. The rear end of the handle connecting mmber is joined through a vibration isolator to the rear end of the rear handle, and the front upper end of the rear handle is joined through a vibration isolator to the top of the engine unit. The upper end of the front handle is positioned in parallel with the upper end of the rear handle in the horizontal direction and joined thereto through a vibration isolator, and the lower end of the front handle is joined directly to the front end of the handle connecting member. The vibration isolators are made of an elastic material such as synthetic rubber and are of the inherent damping type which dampens and absorbs the vibrations by internal hysteresis, i.e., shearing stresses and strains in the vertical direction of the vibration isolators.
Hoeppner, U.S. Pat. No. 4,135,301, discloses a chain saw comprising a handle-housing member including at least one handle for carrying the saw; at least one crankcase member; and at least one means including a vibration-damping elastic member for providing a shock absorbing connection between the housing member and the crankcase member.
Zimmerer, et al, U.S. Pat. No. 4,138,812, discloses a vibration isolating system for chain saws characterized by a handle assembly connected to one side of a vibration generating assembly of a chain saw by a pair of resilient suspension means, with cross-over linkage means being operable to transmit force from the handle assembly to the other side of the vibration generating assembly, across the top of the engine means of this assembly.
Muller, U.S. Pat. No. 4,236,310, discloses a portable motor-driven working implement, e.g., a brush cutter, which includes a first implement part subject to vibrations which is connected to a second implement part on the other side of a handle of the implement through the inter position of at least one elastic insulating element, the rigidity characteristic of the insulating element being adjustable.
Johansson, U.S. Pat. No. 4,285,309, discloses a portable chain saw wherein the rear handle is, at least in part, connected to the vibration generating assembly by a pair of rubber anti-vibration members which are formed as cylinders with annular rings thereabout. These anti-vibration members are positioned in corresponding recesses in the vibrating assembly.
Takahashi et al, U.S. Pat. No. 4,411,071, discloses a chain saw wherein an imaginary line passing between a front mount and a rear mount appears to pass above the crankshaft axis of the engine, however, the engine in this reference is disposed horizontally (the cylinder axis is disposed parallel to the chain saw guide bar).
Von Hardenberg, Canadian Patent No. 985,251, discloses an engine mounting arrangement for an aircraft. The engine mounting arrangement includes front and rear mountings. The rear mounting includes a lower mount having near zero lateral restraint and an elastic vertical restraint and an upper mount having near zero vertical restraint and an elastic lateral restraint. The upper mount of the rear mounting is located vertically such that an imaginary straight line passing through the front mounting passes through the center of gravity of the engine. This mounting arrangement tends to place lateral inputs resulting from vibratory motion of the aircraft fuselage at a point on a line drawn through the front mounting and the center of gravity of the engine. This will inhibit the introduction of fuselage-induced roll moments to the engine. With this decoupling of the engine roll mode from air frame excitation, the engine response is predicted as being well within the manufacturers specified limit for virtually all flight conditions.
Other patents concerned with the damping of vibrations in chain saws include Stihl, U.S. Pat. No. 3,651,839; Heermann, U.S. Pat. No. 3,772,784; Dobbertin et al, U.S. Pat. No. 3,224,473; Kobayashi, U.S. Pat. No. 3,525,373; Nagashima, U.S. Pat. No. 4,202,096; and Dirks, U.S. Pat. No. 4,296,553.
As may be readily ascertained from the above discussion, the art continues to seek effective means for damping the vibrations caused by an internal combustion engine in a hand-held power tool.